166 



ASt'OMYCKTES. 



This is supported by Smith's investigations, in which an an- 

 atomical comparison of diseased twigs of peach and ahuoiid 

 showed no difference in the pathological effects. 



Exoascus crataegi Fuck, occurs on Crataegus Oxyavantha , 

 and causes red swellings on the leaves and flowers, accom- 

 panied l)y hypertrophy of shoots in which the mycelium 

 perennates. 



Exoascus Tosquinetii (West.). The deformation caused by 

 this species is frequent on the black alder (Alnv.s glutinosa). 

 The thickened, elongated, wrinkled twigs render attacked parts 

 very conspicuous in contrast to the normally developed parts of 



the tree. The leaves may l)e 

 wholly attacked and much 

 enlarged, or they may only 

 be hypertrophied at places so 

 as to form pustule-like swell- 

 ings. The epidermal ami 

 mesophyll- cells of diseased 

 leaves become greatly en- 

 larged. 



Exoascus aureus (Pers.). 



The leaves of the black poplar 



(Pojn'/vs iiigra) attacked by 



this parasite exhibit pustides 



(Fig. 62). The asci are 



formed as a golden coating 



fin the concave side of the 



])ustules, which is, in most 



cases, the under side of the 



leaf, rarely the upper. The 



cells forming the pustules 



have thicker walls and a 



somewhat different shape from the normal epidermal cells, and 



they are not unfrequently sub-divided by walls of secondary 



origin (Fig. 63). 



According to .Smith, the cells of the palisade parenchyma have 

 also thickened walls, as well as behig elongated and occasionally 

 chambered ; the cells of the spongy parenchyma are enlarged and 

 have thicker walls ; so also are the cells of the collenchyma of 

 the leaf venation. 



Leaf of Po'iiut-us 



Fui. C'i. — h'joannis o; 

 niyru, showinp the ptistulc-like swellings.' 

 Tnbeiif del.) 



